CP 8.1.1 Startup Failure: Connect REST API Timeout

by Alex Johnson 51 views

This article discusses a recent failure encountered while starting Confluent Platform (CP) version 8.1.1 in a mdc-sasl-plain environment. The issue stems from a timeout while waiting for the Connect REST API to become ready. We'll delve into the logs, analyze the potential causes, and explore troubleshooting steps to resolve this problem.

Understanding the Issue

The core issue revolves around the connect-us container failing to start within the allocated 300-second timeframe. The logs clearly indicate this with the message: the connect REST API is still not ready after 300 seconds, see output. This timeout suggests a problem either with the Connect service itself or with its dependencies, preventing it from initializing correctly.

The failure occurred within the context of the start.sh script execution, specifically within the environment/mdc-sasl-plain directory of the kafka-docker-playground project. The project utilizes Docker containers to simulate a Confluent Platform deployment, making it a valuable tool for testing and development. The error indicates a potential issue with the configuration or the environment setup within this specific scenario.

Analyzing the Logs

The provided logs offer valuable clues to pinpoint the root cause. Let's break down the key sections:

1. Initial Setup and Configuration

The logs reveal that the environment is being set up in Kraft mode (Starting up Confluent Platform in Kraft mode as ENABLE_KRAFT environment variable is set), which is a modern consensus mechanism for Kafka that eliminates the need for ZooKeeper. Several services are explicitly disabled, including ZooKeeper, Control Center, Flink, ksqlDB, REST Proxy, Grafana, kcat, and Conductor. This narrowed scope simplifies the environment but also highlights the importance of the remaining services functioning correctly.

2. Replicator Installation

An attempt to install the Replicator component (confluentinc/kafka-connect-replicator:8.1.1) initially failed. The system then tried installing the Replicator with the default tag 8.1.0, which succeeded. This suggests a possible issue with the availability or compatibility of the 8.1.1 version of the Replicator at the time of the test. While this may not be the direct cause of the Connect timeout, it indicates potential inconsistencies in the environment setup.

3. Container Startup Sequence

The logs show the sequence in which Docker containers are created and started. Containers such as prometheus-c3-v2, controller-us, controller-metrics, controller-europe, broker-metrics, broker-us, broker-europe, connect-us, schema-registry-us, connect-europe, and schema-registry-europe are started in a specific order. The connect-us container is crucial for Kafka Connect functionality, which is responsible for data integration between Kafka and other systems.

4. Connect REST API Timeout

The critical error message the connect REST API is still not ready after 300 seconds clearly indicates that the Connect service within the connect-us container failed to initialize properly within the allotted time. This usually implies that the Connect worker process either failed to start, encountered an unrecoverable error, or is experiencing a prolonged delay in initialization.

5. Broker Errors: Invalid Replication Factor and Telemetry Issues

The logs from broker-europe, broker-us, and broker-metrics show errors related to cluster link metadata topic creation failures (org.apache.kafka.common.errors.InvalidReplicationFactorException) and inability to submit telemetry events (io.confluent.telemetry.events.exporter.http.HttpExporter). The InvalidReplicationFactorException suggests that the replication factor configured for internal topics (likely related to cluster linking) is higher than the number of available brokers. This is a significant issue, especially in a multi-broker setup, as it can lead to data loss and cluster instability. The telemetry errors, while not directly related to the Connect timeout, indicate a potential problem with Confluent's telemetry service connectivity.

6. Controller Errors: Telemetry and Data Balancing

Similar to the brokers, the controller-metrics, controller-europe, and controller-us logs show errors related to telemetry submission. Additionally, the controller-europe and controller-us logs exhibit Uncaught exception in SBK_DataBalanceEngine-0, which points to a potential issue with the Self-Balancing Kafka (SBK) functionality. SBK is responsible for automatically balancing data across brokers, and errors in this component can affect overall cluster health.

Potential Causes and Troubleshooting Steps

Based on the log analysis, several potential causes could contribute to the Connect REST API timeout:

  1. Insufficient Resources: The connect-us container might not have sufficient CPU or memory resources to start correctly. This is especially relevant if the host machine is under heavy load or the container resource limits are set too low. Troubleshooting: Check the resource utilization of the host machine and the resource limits configured for the connect-us container in the Docker Compose file. Increase the resources if necessary.

  2. Networking Issues: Connectivity problems between the connect-us container and other services (e.g., Kafka brokers, Schema Registry) could prevent Connect from initializing. Troubleshooting: Verify that the Docker network is configured correctly and that the connect-us container can communicate with other containers using their respective hostnames and ports. Use tools like docker exec to access the container and test network connectivity with ping or telnet.

  3. Configuration Errors: Incorrect configurations within the Connect worker properties file (e.g., incorrect Kafka broker addresses, Schema Registry URLs, or security settings) can lead to startup failures. Troubleshooting: Examine the Connect worker configuration files (usually located in /etc/kafka/connect-distributed.properties or /etc/kafka/connect-standalone.properties within the container) and verify that all settings are accurate. The logs mention the command playground container get-properties -c <container>, which can be used to inspect the actual properties file.

  4. Dependencies Not Ready: Connect might depend on other services (e.g., Kafka brokers, Schema Registry) being fully initialized before it can start. If these dependencies are not ready, Connect might time out while waiting for them. Troubleshooting: Ensure that the startup order of containers in the Docker Compose file reflects the dependencies. The logs indicate the startup sequence, but it's crucial to confirm that dependencies are fully operational before Connect attempts to initialize. You can use health checks within Docker Compose to enforce dependency readiness.

  5. Kafka Broker Issues (Replication Factor and Telemetry): The InvalidReplicationFactorException in the broker logs suggests a misconfiguration in the replication factor settings, especially in a multi-broker environment. This could affect Connect's ability to create internal topics or perform essential operations. The telemetry errors might not directly cause the timeout but could indicate a broader issue with the environment's connectivity or configuration. Troubleshooting: Review the Kafka broker configurations (e.g., server.properties) and ensure that the replication factor settings are appropriate for the number of brokers in the cluster. Investigate the telemetry configuration and network connectivity to Confluent's telemetry service.

  6. SBK Issues: The errors related to the Self-Balancing Kafka (SBK) functionality in the controller logs could potentially impact cluster stability and, indirectly, Connect's ability to function correctly. Troubleshooting: Examine the SBK configuration and logs for more specific error details. Consult Confluent's documentation and support resources for guidance on troubleshooting SBK issues.

  7. Replicator Installation Issue (Initial Failure): While the Replicator installation eventually succeeded with the 8.1.0 tag, the initial failure with 8.1.1 suggests potential problems with Confluent Hub or the availability of specific component versions. This might indicate temporary network issues or repository inconsistencies. Troubleshooting: Verify network connectivity to Confluent Hub and retry the Replicator installation with the desired version (8.1.1). If the issue persists, consider using a specific version that is known to be stable and compatible with your Confluent Platform setup.

Resolution Steps

To resolve the Connect REST API timeout issue, I recommend the following steps:

  1. Check Resource Limits: Ensure that the connect-us container has sufficient CPU and memory resources.

  2. Verify Network Connectivity: Confirm that the connect-us container can communicate with other containers, especially the Kafka brokers and Schema Registry.

  3. Inspect Connect Configuration: Examine the Connect worker configuration files for any errors or inconsistencies.

  4. Ensure Dependency Readiness: Verify that Kafka brokers and Schema Registry are fully initialized before Connect attempts to start. Implement health checks in Docker Compose to enforce dependency readiness.

  5. Address Replication Factor Issue: Review the Kafka broker configurations and correct any misconfigurations related to replication factors.

  6. Investigate SBK Errors: Examine the SBK logs and configuration for more specific error details. Consult Confluent's documentation and support resources.

  7. Retry Replicator Installation (Optional): If the Replicator installation failure is a concern, retry installing the desired version (8.1.1) after verifying network connectivity to Confluent Hub.

  8. Collect Detailed Logs: Use the playground container logs --open --container connect command (as suggested in the logs) to gather detailed logs from the connect-us container. These logs can provide more specific error messages and stack traces that can aid in troubleshooting.

By systematically addressing these potential causes and following the troubleshooting steps, you should be able to identify and resolve the Connect REST API timeout issue and successfully start Confluent Platform in your mdc-sasl-plain environment.

Conclusion

The Connect REST API timeout issue in Confluent Platform 8.1.1 highlights the importance of careful configuration, dependency management, and resource allocation in distributed systems. By analyzing the logs, identifying potential causes, and following a systematic troubleshooting approach, you can effectively resolve such problems and ensure the smooth operation of your Kafka Connect deployments.

For further information on Confluent Platform and Kafka Connect, consider exploring the official Confluent documentation: https://www.confluent.io/